Gripping mechanism for a lifting fork



May 9, 19M s. l.. HlRscHBoEcK 2,983,397

GRIPPING MECHANISM FOR A LIFTING FORK Filed Sept. 29, 1958 2 Sheets-Sheet 1 IIIIIIIL Attorneys May 9, 1961 s. L. HlRscHBoEcK 2,933,397

GRIPPING MECHANISM FOR A LIF'TING FORK Filed Sept. 29, 1958 2 Sheets-Sheet 2 FIG. 7

IN VENTOR.

STEPHEN H/HSGHBOEGK Aftorneys 2,983,397' GRLPPING MECHANISM FoR A LIFTING FORK Stephen L. Hirschhoeck, P.0. 130x118, Omro, Wis.

Filed Sept. 29, 1958, Ser. No. 763,959

9 Claims.A (Cl. 214-655,)

This invention relatesto a gripping mechanism for a l1fting fork as may be employed on a fork lift truck and more particularly to self-actuated gripping means for an Y unpalletized load.

'I'he invention isy -applied to a fork tine arrangement adapted to lift and transport an unpalletizedload wherein the square of rectangular units such as boxes, bricks or the like are stacked inY a plurality of courses. The lowermost course of the stack is provided with one or more parallel spaces in accordance with the number of fork tines employed which together with the next adjacent course forms spaced tunnels for receiving the tines in preparation for lifting and transporting the stack. In effect, the spaced units in the lowermost course together with the fork tines serve asv/the base or support for the remainder of the stack eliminating the need for pallets or the like. l

The fork tines for` handling such unpalletized loads generally'include laterallyv movable gripper bars which are adaptedy to engage the sides of the spaced units in the lowermost course and apply adequate pressure for the support of the units between the tines. Heretofore, the gripper bars have generally been hydraulically or pneumaticallyoperated requiring a plurality of relatively long lengths of flexible tubing,v -appropriate remote controls for the operator and pressurizing equipment. Such installations are costly and require considerable, space for mounting and for accommodating the lengths of flexible tubing.. Furthermore, such installations include a considerable amount of equipment, any portionof which can fail from time to` time, and doesg to immobilize the fork lift unit until appropriate repairs have been made.

According to this invention, the laterally movable gripper bars for the fork tines handling unpalletized loads are self-actuated and. generally include depressible` platform means spacedA above the tine which is depressed in response to a loadthereon. Actuating means. connect the nited States Patent platform means and the gripper bar whereby the bar is v moved` toan extended position inV responseto the load imposed on the platformY means. .Means are further provided toretract the gripper bar and return the platform meansto its raised position upon removal of the load.

The accompanying drawings illustrate the best mode for carrying out the invention as presently'contemplated and set forth hereinafter.

In the drawings:

Figure 1 is a perspectiveview of a fork lift truck equipped with fork tines` havingl the self-actuated gripping mechanism` of this invention;

Fig. 2 is a partial end elevation of a` fork lift truck and shows the tines, of` this invention supporting` an unpalletized load;

Fig. 3v is a side elevation. of a fark;` tine. with; parts broken away andsectioned tp. shgmr the-.gripping-'mechaf y nism of this invention;

Fig. 4` is a view taken online of Biggfyand additionally includesfpartial `unita-of the. unpalletiadload;

Fig. S is a view similar to Fig. 4-showing the gripper bar in its extended position;

Fig. 6 is a partial sectional view taken on line 6-6 of Fig. 4;

Fig. 7 is an enlarged cross sectional view taken on line '7-7 of Fig. 6; and

Fig. 8 is a view similar to that of Fig. 4 and shows the mechanism for another embodiment of the invention.

Referring to the drawings, the fork lift truck 1 includes a forwardly disposed vertical carriage 2 which is adapted to be raised andlowered by means of an elevator 3 mounted on the truck. A plurality of transversely spaced fork arms or tines 4 extend forwardly from the lower portion of the carriage 2 at substantially right angles to the carriage. As shown, each tine 4 may include a rearwardly disposedV vertical portion 5 having a transversely extending Tshaped projection 6 rearwardly thereof .for slidably engaging a corresponding T-shaped slot 7 in the forward face of the carriage 2 for support. The vertical portion 5 of each tine 4 may further include a rectangular projection 8 spaced above projection 6 and engaging the recess 9 in the face of rthe carriage 2'. The projection 8 of each tine portion 5 is provided with a hole 410 and a transversely extending shaft 11 extends through the aligned holes 10 of the respective tines and is removably secured to the carriage 2. Means, not

shown, are generally provided for slidably moving the tines 4 transversely of carriage 2 within the slot 7 and recess 9 and on shaft A11 to provide the desired spacing between the tines.

The horizontal portion 12 of tines 4 comprises generally elongated channel section members 13 having` a vertically disposed web 14 and spaced horizontal anges 15 and 16. The two outermost tines 4 each includebut a single channel section member 13 as shown in Fig, 5, kand have their respective webs 14 disposed outwardly and the open side of the channel members facing inwardly. The inner tine 4 includes a pair of channel section members 13 having their respective webs disposed back-fto-back and secured together and with the open sides of the channel members facing in opposite directions.

As shown in Fig. 5, a laterally movable gripper bar 17 is disposed in the open side of channel member 13 and extends substantially over the full length of the channel member. The outer surface 18 of the gripper bar is lined with a friction material such as rubber or the like to provide a good gripping surface. The bar 17 is sup,- ported in spaced relation from flanges 1-5 and 16 and in the retracted position the outer surface thereof is generally in alignment with the outer edges of the flanges.

A plurality of longitudinally spaced cylindrical rods 19 provide support for. the bar 17. 'Ihe rods 19 are slidably disposed within tubular guide members 20 which yare secured to the web 14 of the channel'member generally midway between the anges 1S and 16. The outer end of each rod 19 is provided with a rounded head 21 and a, circumferential V-shaped groove 22 is spacedim wardly from the head. The heads 2.1 of rods 19 are received in slots 23 provided in corresponding projections 24 on the inner surface of gripper b ars 17. kThe opening of. each slot 23 is restricted to receive groove 22 of the rods. The depth of the slots 23 is such as to permit limited vertical articulation of the gripper bar 17 on the rounded heads 2K1.

According to Figures 3 through 6, the gripper bar 17 is actu-ated laterally by means of a depressible platform member 25 through the mechanical linkage mechanism 26, connectingthe gripper bar and the platform member.

The platform member 25 extends generally over the length of channel member 13 and is normally disposed in spaced relation above. upper iiangen 15 of the channel,

Member 25 is carried by a plurality of vertically extending rods 27 which are slidable within corresponding guides 28 mounted vertically in the channel member 13. The linkage mechanism 26 connecting the platform member 25 and the gripper bar 17 'comprises a bell crank 29 including the' pivotable shaft '30 journally received between longitudinally spaced brackets 31 mounted within channel member 13 to the lower flange 16.' The bell crank 29 further includes a pairof angularly spaced arms 32 and 33 `which are tixedly secured on shaft .itl and pivot therewith. One end of linkage member 34 is pivotally secured to the outer end of arm 32. The other end of linkage member 34 is pivotally secured to an inwardly extending projection 35 provided on gripper bar 17 in transverse alignment with bell crank arm 32 and substantially midway between the longitudinal edges of the bar. The outer end of bell crank arm 33 is pivotally secured to one end of linkage member 35. A depending projection 37 extends downwardly from platform member 25 into the channel member 13 through an opening 38 in upper flange 15 inyertical alignment with bell crank arms 33 and is pivotally connected to the other end of linkage member 36 to complete the linkage. As shown in Fig. 5, depression of platform member 25 effects pivoting of the bell crank 29 to move the gripper bar 17 to an extended position. Retraction of the gripper bar 17 is effected by a plurality of longitudinally spaced tension springs 39 which are secured respectively to the gripper bar generally midway between the longitudinal edges thereof and the web 14 of channel member 13 generally midway between anges l and 16. Retraction of bar 17 in turn pivots bell crank 29 to return the platform member 25 to the position spaced above flange 15.

In operation, a fork lift truck equipped with tines in accordance with this invention, is maneuvered into position placing the tines 4 in the spaced tunnels ofthe unpalletized stack. The carriage 12 is then raised by the elevator 3 bringing the platform member 25 into engagement with the underside of the units in the second course of the stacked load. As the tine continues to move upwardly, the platform member 25 is depressed and the gripper bar 17 is moved to an extended position against the pressure of spring 39 to engage the side of the adjacent stack unit in the loweimost course. The adjuhtment between gripper bar 17 and the platform member 25 should be such that the bar will be firmly engaged to the adjacent stack unit before the platform member reaches the bottom of its travel so that the weight of the stack will assure Vadequate and continued lateral gripping pressure on the bar. With the gripper bars 17 onl tines 4 irmly engaged with the stack units in the lowermost course, the tines together with the units in lowermost course provide a rigid base or support for lifting and transporting the entire stack load as shown in Fig. 2 to eliminate the need for pallets or the like.

It frequently occurs that the stack units are not truly rectangular and that upon application of pressure by the gripper bar on the units of the lowermost course the sides engaged by the bar are forced to a slight angularity. This angularity is usually compensated for by the limited articulation permitted by the gripper bar 17 relative to the rods 19 to assure contact by the bar over its entire vertical extent.

After the stack load has been transported to the selected location, the tines 4 move downwardlyrwith the carriage 2 to deposit the stack load. After downward movement of the stack load is interrupted, the weight on platform members 25 is removed as the tines 4 continue downwardly and the springs 39 retract the gripper vbar 17 and return the platform member to its original spaced position above ange 15.

In the embodimenut of the invention shown in Fig. 8, the mechanical linkage mechanisms 26 hereinbefore described are replaced by hydraulic linkages 4d. As shown,

a vertically disposed cylinder 41 is secured to lower flange 16 within channel member 13 and a vertical moving plunger 42 is disposed therein. A connecting rod 43 rigidly secured at one end to the underside of platform member 25 extends downwardly through opening 38 in upper tiange 15 and has the opposite end thereof rigidly secured to the plunger 42. A second cylinder 44 is horizontally disposed and secured to the web 14 of the channel midway between the flanges 15 and 16. r[ 'he plunger 45 is disposed in cylinder 44 and a connecting rod 46 is rigidly secured thereto and extends outwardly therefrom. The end of connecting rod 46 opposite from plunger 4S is pivotably secured to the inwardly extending projection 35 on the gripper bar 17. A fluid transfer conduit 47 connects the lower end of cylinder 41 with the inner end of cylinder 44 so that oil or a similar hydraulic tluid may ow unrestricted therebetween. lnitially hydraulic uid is introduced into linkage 40 lling the transfer passage 47 and the cylinders 41 and 44 ahead of the respective plungers 42 and 45; While cylinders 41 and 44 are not necessarily of the same dimensions, their displacement volume must be equal to accommodate the duid transferred from one cylinder to the other.

In operation, depression of platform member 25 of Fig. 8 displaces hydraulic fluid from cylinder 41 to cylinder 44 to move the gripper bar 17 to an extended condition engaging the side of the adjacent stack unit. When the load on platform member 25 is removed, the tension spring 39 effects retraction of the gripper bar 17 displacing the hydraulic fluid from cylinder 44 back in to cylinder41 and raises the platform member to its initial position spaced above ilange 15.

The invention thus provides a self-actuated gripper mechanism for handling unpalletized loads, eliminatlng the need for remotely controlled equipment as now commonly used.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

I claim:

l. In a' fork tine for a fork lift truck or the like, a gripping member disposed to one side of the tine, means carried by the tine for supporting and guiding the gripping member for reciprocation in a horizontal plane be-A tween an extended position and a retracted position, platform means disposed in spaced relation above said tine and being depressible in response to a load imposed thereon, linkage means connecting the platform means and said gripping member whereby said member is moved to theV extended position when a load is imposed on said platform means to depress same, and means to retract said gripping member and raise said platform means to its origin-al position upon removal of the load.

2. The combination set forth in claim 1 wherein the means connecting the platform means and the gripping member is a mechanical linkage including a bell crank pivotally mounted Within the tine. j

3. The combination set forth in claim 1 wherein the means connecting the platform means and the gripping member is `a closed hydraulic linkage comprising a first cylinder having a plunger operable by the platform means, a second cylinder having a plunger connected to the gripping member, and uid passage means connecting the cylinders whereby uid is displaced from the rst cylinder when a load s imposed on the platform means to `actuate the plunger in the second cylinder and thereby move thegripping member to the extended position;v

4. In a lifting fork for a fork lift truck orthelike,` a tine having a laterally facing open side', a gripper bal disposed in s aid open side, means carried within the tine for supporting and guiding the gripper bar for reciprocation in a horizontal plane between an extended positionand a retracted position, a linkage mechanism supported within the tine and having one end thereof connected to the gripper bar and adapted to move the gripper bar to an extended position for engaging an object to be lifted, platform means disposed above said tine and being depressible in response to a load imposed thereon and connected to the other end of the linkage mechanism whereby the linkage mechanism is actuated to move the gripper bar to the extended position, and means to retract the gripper bar upon removal of the load on said platform means to disengage the gripper bar from the object.

5. In a -lifting fork for a fork lift truck or the like, a tine having a laterally facing open side, a gripper bar disposed in said open side, extendible means connected respectively to the tine and gripper bar Ito support and guide the gripper bar 'for reciprocation in a horizontal plane and provide for vertical -articulation of the bar relative to the tine, a linkage mechanism supported within the tine and having one end thereof connected to the gripper bar and adapted to move the gripper bar to an extended position for engaging an object to be'lifted, platform means disposed above said tine and being depressible in response to a load imposed thereon and connected to the other end of the linkage mechanism whereby the linkage mechanism is actuated to move the gripper bar to the extended position, and means to retract the gripper bar upon removal `of the load on said platform means to disengage the gripper bar from the object.

6. In a lifting fork for a fork lift truck or the like, a tine having a vertical wall and a laterally facing open side opposite from said wall, a gripper bar disposed in said open side, telescoping support means connecting the gripper bar and vertical wall to support the gripper bar for reciprocation in a horizontal plane, a linkage mechanism supported within the tine and having one end thereof connected to the gripper bar and adapted to lmove the gripper ybar to an extended position for engaging Van object to be lifted, plaform means disposed above said tine and being depressible in response to a load imposed thereon and connected to the other end of the linkage mechanism whereby the linkage mechanism is actuated to move the gripper bar to the extended position, and a tension spring connecting the vertical wall and the gripper bar to retract the gripper bar upon removal of the load on said platform means to dsengage the bar from the object.

7. In a lifting fork for a fork lift truck or the like, a tine having a vertical wall and a laterally facing open side opposite from said Wall, a laterally movable gripper ba-r disposed in saidopen side, a tubular member secured to the vertical wall land extending horizontally in the direction of the open side, a. plunger having one end thereof disposed slidably in said tubular member, the other end of said plunger being connect-ed to the'gn'pper bar to support the bar and having a rounded head providing for vertical articulation of the gripper bar-rela'- tive to said head, a linkage mechanism supported within the tine and having one end thereof connected to the gripper bar and adapted to move the gripper bar to an extended position for engaging an object to `be lifted, platform means disposed above said tine and being depressible in response to a load imposed thereon and connected to the other end of the linkage mechanism whereby the :linkage mechanism is actuated to move the gripper bar to the extended position, and a tension spring connecting the vertical wall and the gripper Ibar to retract the gripper bar upon removal of the load on said platform means to disengage the bar from the object.

8. The combination set forth in claim 7 wherein the connections of the plunger, linkage mechanism and tension spring, respectively, to the gripper bar are generally horizontally aligned on a plane substantially midway between the vertical extent of the gripper bar.

9. In a lifting fork for a fork lift truck or the like, a tine having a vertical wall and a laterally facing open side opposite from said wall, a laterally movable gripper bar disposed in said open side, a guide tube secured to the Vertical wall and extending horizontally in the direction of the open side, a plunger having one end thereof disposed slidably in said guide tube and the other end of said plunger being connected to the gripper bar, a linkage mechanism operably supportedl within the tine and having one end thereof connected to the gripper bar and adapted to move the gripper `bar to an extended position for engaging an object to be lifted, the connections of the plunger and linkage t mechanism to the gripper bar being generally horizontally aligned on a plane substantially midway between the Vertical extent of the gripper bar, platform means disposed in spaced relation above said tine and being depressible in response to a load imposed thereon and connected to the other end of the linkage mechanism whereby the linkage mechanism is actuated to irnove the gripper bar to the extended position,` and meansV to retract said gripper bar and raise said platform `means to its original position spaced above said tine upon removal of the load.

References Cited in the file of this patent UNITED STATES PATENTS -France .a Sept. 1, 1954 

